In motor vehicles, the battery is normally charged from a polyphase alternator, generally a three-phase alternator, feeding a diode rectifier bridge to generate a rectified alternator voltage for charging the battery. The amplitude level of the rectified alternator voltage, or the charging voltage level applied to the battery, is regulated by means of a regulator which regulates the excitation current Ie applied to the rotor of the alternator, and in particular which regulates the duty ratio of the excitation current, on the basis of detecting the alternator phase voltage as delivered by one of the stator windings of the three-phase alternator.
Regulators of this type are well known in the art and give satisfaction under normal conditions of use. They are generally classified as belonging either to a first category of "multifunction" regulators or to a second category of "mono-multifunction" regulators or "dual-purpose" regulators suitable for being used in vehicles which are wired for monofunction regulators or in vehicles which are wired for multifunction regulators.
Wiring diagrams for these types of regulators are given in accompanying FIGS. 1a and 1b. The essential difference between multifunction regulators and dual-purpose regulators, as can be seen from the above-specified figures, results from the need with multifunction regulators to close the vehicle ignition key switch in order to enable the regulator to operate since the rotary field winding of the alternator is fed with excitation current via the ignition key switch.
For a more detailed description of a multifunction type regulator, reference may be made to U.S. Pat. No. 4,584,515 (Edwards) granted Apr. 22, 1986.
Regardless of the category to which regulators may belong, they nevertheless suffer from various operating faults caused by interference voltages or potentials appearing on the windings of the alternator. These interference voltages or potentials may be generated either by equipment belonging to the motor vehicle, e.g. a revolution counter directly connected to the stator windings of the polyphase alternator, or else due to the presence of insulation faults enabling leakage resistances to appear and thus interference bias potentials to appear at the rectifier bridge and at the stator windings, with the leakage resistances being formed, for example, by salt bridges. Such leakage resistances are represented by dashed lines in FIGS. 1a and 1b.
Thus, the above-mentioned leakage resistances and interference potentials may bias the windings of the alternator stator to a value making it appear that the alternator rotating even though the alternator is stationary, and this may be misinterpreted by a regulator connected in conventional manner to the stator windings of a three-phase alternator.
In addition, when the alternator is rotating in the absence of excitation current, as may occur when the vehicle is started, for example, an electromotive force appears at the outputs of the alternator stator windings due to the remanence of the magnetic circuits. This electromotive force as normally detected by a conventional regulator such as shown in FIG. 1a or 1b, serves to indicate that the polyphase alternator is rotating and to enable the regulator to apply excitation current to the rotary field winding of the alternator. The above-mentioned leakage resistances and interference potentials may then have the effect of stabilizing the output voltage from the phase winding which is connected in conventional manner to the regulator, and this may be erroneously interpreted by the regulator as indicating that the alternator is stationary.
With multifunction regulators, a fault in detecting the amplitude of the alternator phase voltage is of minor importance since the regulator operates or not, i.e. regulates the excitation current to the rotary field winding of the alternator, under direct control of the vehicle ignition switch opening or closing, and this is fully under the control of the user.
However, when the same alternator is stationary, and when leakage resistances are present as shown in FIG. 1, then the alternator phase voltage input to the regulator may be biased to a value whose amplitude corresponds to rotation of the alternator. Such a situation can be objectionable if the user happens to close the ignition switch in order to switch on auxiliary circuits in the vehicle, i.e. put the ignition key in an intermediate position provided for that purpose, while the vehicle, its engine, and the alternator are all stationary.
With dual-purpose regulators, leakage resistances and interference potentials may provide erroneous information to the regulator causing it to deliver excitation current to the alternator while the alternator is not rotating, or conversely, failing to trip the regulator once the alternator is in rotation.
The object of the present invention is to remedy the above-mentioned drawbacks by providing a detector circuit for detecting a phase signal of a polyphase alternator for a battery charge regulator in a motor vehicle in which a symmetrical connection relative to the stator windings of the alternator makes it possible to reduce or eliminate interference voltages generated by motor vehicle auxiliary equipment which is directly connected to the stator windings of the alternator.
Another object of the present invention is to provide a detector circuit for detecting a phase signal of a polyphase alternator for a battery charge regulator in a motor vehicle in which the low value of the impedence of the stator windings of the alternator serves to reduce or eliminate the effects of leakage resistances that may form on the rectifier bridge connected to the alternator.